How did Hey Arnold's parents die?
Hereof, what really happened to Arnold's parents?
Since fans met Arnold when Hey Arnold! Who his parents were or where they went wasn't even addressed until the show's Season 3 episode "Parents Day," in which it was revealed that Arnold's parents were explorers and had disappeared on a humanitarian mission to San Lorenzo, along with the plane that was carrying them.
Beside above, did Hey Arnold find his parents?
In the movie, Arnold battles pirates to find his parents. It turns out they're ill with sleeping sickness. Arnold, Gerald, and Helga somehow figure out the cure for the illness. They save his parents and the whole village, and he finally brings his parents home to the boarding house in New York.
According to The Hey Arnold Theory the true story behind Hey Arnold starts with the city that he lives in. The city the real Arnold lives in is actually a mostly poor area of New York and the real Arnold is just a poor orphan living with his grandparents Gertie and Phil. Well, at least he believes he's an orphan.